Primary cultures of fetal hepatocytes from Zucker obese (fafa) and lean (FaFa) rats will be studied to determine if there are differences in growth potential and in lipogenic activity between cultures derived from livers with a gene frequency of 1.0 Fa and those with a gene frequency of 0.75 fa. Total lipid synthesis will be measured in cultures incubated for 24 hours with 3H2O and 14C-alanine. Cloning techniques will be used to isolate a variety of cell types derived from stromal fractions of adipose tissue digests from Zucker obese and lean rats. We hope to isolate clones capable of lipid accumulation. Characterization of these cell types from Zucker rats in respect to growth potential and metabolic activity, particularly lipogenesis, may enhance our understanding of the primary lesion which results in obesity in this animal model. Elucidation of the etiology of hyperplastic obesity in the Zucker fatty rat may aid our understanding of the similar syndrome seen in human obesity of early-onset.